Hydrolysis of hydroxybenzoate saxitoxin analogues originating from Gymnodinium catenatum

The paralytic shellfish poisoning (PSP) toxin producer Gymnodinium catenatum produces several hydrophobic analogues of saxitoxin (STX). These are poorly studied due to their recent discovery and lack of standards. It was previously observed these hydrophobic analogues could be partially hydrolysed, loosing its benzoate moiety during alkaline oxidation to obtain fluorescent products measurable by HPLC analysis. The hydrolysis reaction was further explored to study two practical aspects. One was the indirect measurement of these compounds through its hydrolysis products: the decarbamoyl analogues of STX. The second one was to simplify standard production of decarbamoyl analogues, which are commonly found in contaminated shellfish products.PSP analogues are unstable in alkaline media. The hydrolysis of benzoate analogues progressed rapidly with increasing base amount, but the decarbamoylgonyautoxin type hydrolysis products were short lived and converted into decarbamoylsaxitoxin type analogues. For a rapid estimation of the presence of these benzoate analogues in seafood, decarbamoylgonyautoxin type analogues can only be measured as decarbamoylsaxitoxin type equivalents.For production of standards, complete hydrolysis of hydroxybenzoate decarbamoylsaxitoxin analogues can render decarbamoylsaxitoxin and decarbamoylneosaxitoxin. Obtaining decarbamoylgonyautoxins was not suitable resorting to decarbamoylgonyautoxin type hydroxybenzoate analogues due to the prolonged reaction times required for complete hydrolysis and their instability at high pH. Hydrolysis of sulphated-benzoate analogues was best suited for obtaining decarbamoylgonyautoxins due to the very rapid hydrolysis time required.

Research highlights
► Gymnodinium catenatum produces several hydrophobic analogues of saxitoxin.
► Hydrophobic analogues can be hydrolysed, loosing its benzoate moiety.
► Hydrolysis of 11-sulphated analogues produces decarbamoylgonyautoxins.
► Hydrolysis of non-11-sulphated analogues produces decarbamoylsaxitoxins.